The present invention relates to audio signal processing systems having a function of transmitting audio signals among a plurality of devices in substantially real time.
In the field of digital mixers, it is known to separately provide a console for operation by a human operator and an engine for performing signal processing, such as mixing processing and construct a mixing system by connecting the engine to the console. It is also known to connect two engines to such a mixing system to realize or implement mirroring of the engines (engine mirroring) and thereby construct a so-called fault-tolerant mixing system (see, for example, Japanese Patent Application Publication No. 2003-101442 which will hereinafter be referred to as “Patent Literature 1”). In such a fault-tolerant mixing system, one of the two engines is normally used as a main signal processing engine while the other engine is used as a backup engine. When abnormality has occurred to the engine being used (i.e., main signal processing engine), switching is made from the main signal processing engine to the backup engine. Such engine switching can be made both automatically and in response to an instruction given by a human operator.
Further, in the fields of WWW (World-Wide Web) servers, online systems and ordinary computer systems, such as routers, it is known to implement a fault-tolerant system. Among conventionally-known ways of implementing a fault-tolerant system in an ordinary computer system is one in which a main device for performing processing at normal times and another device for backing up the main device are provided so that the backup device takes over the operation or role of the main device when some abnormality has occurred to the main device.
Also, there have heretofore been known audio networks capable of transmitting audio signals (audio signals) among a plurality of devices (nodes) interconnected via a network. Examples of a technique for realizing such an audio network include CobraNet (registered trademark), EtherSound (registered trademark), etc. (see, for example, 1) “What's CobraNet™?” [online], BALCOM Co. Ltd. [searched on Jun. 23, 2009], Internet <URL: http://www.balcom.co.jp/cobranet.htm> (hereinafter referred to as “Non-patent Literature 1”); and 2) “EtherSound (outline)”, [online], Bestec Audio Inc. [searched on Jun. 23, 2009], Internet <http://www.bestecaudio.com/download/EtherSound_Overview.pdf> (hereinafter referred to as “Non-patent Literature 2”)).
Japanese Patent Application Publication No. 2008-072347 (hereinafter referred to as “Patent Literature 2”), for example, discloses a audio signal processing system in which a plurality of devices (nodes) are interconnected via network cables of the Ethernet (registered trademark) standard, and in which a “transmission frame” having audio signals put therein are transmitted among the plurality of notes by the “transmission frame” having the audio signals making a tour, per sampling period, through all of the nodes connected to the network. With the disclosed audio signal processing system having such an audio network technique applied thereto, audio signals of as many as hundreds of channels can be transmitted among the plurality of nodes in substantially real time by use of a plurality of transmission channels of the transmission frame. Further, with the transmission frame, the disclosed system can transmit control data etc. of the Ethernet (registered trademark) standard simultaneously with the audio signals.
Among possible embodiments of the aforementioned audio signal processing systems are, for example, large-scale mixing systems for use in concert venues, theaters, music production studios, public address systems and the like, intercommuication systems for communicating audio signals among communication units each including a microphone and audio system, effect impartment systems for imparting effects to audio signals of musical instrument performance tones and the like, plural-track recording/reproducing systems capable of simultaneously recording/reproducing a plurality of audio signals, etc.
However, with the fault-tolerant mixing system disclosed in Patent Literature 1, audio signal input and output devices have to be connected to the two engines via cables in the same wiring configuration; namely, audio signal transmitting wiring has to be physically dualized, which tends to make the wiring operation very cumbersome.
Further, there has been known no good method for effectively constructing a fault-tolerant system in the case where a audio signal processing system which transmits audio signals among a multiplicity of nodes as disclosed in Non-patent Literatures 1 and 2 is to be built. For example, even if the method presently used in ordinary network equipment, such as WWW servers, is applied to the audio signal processing system, a considerable time is required for causing the backup device to take over the operation of the main device where a trouble or abnormality has occurred, and thus, transmission of audio signals would be undesirably broken while the role of the main signal processing engine is switched to the backup engine.
Particularly, with audio signal processing systems for use in environments, such as music festival venues or various event venues, where music etc. are presented to a lot of audience, it is important that audio signals continue to be output with no substantive interruption or break, and thus, in order to effect mirroring of devices, such as engines, there is a need to allow a backup device to take over the operation of a main device with no substantive break in output audio signals (i.e., with no substantive sound break). However, where the conventionally-known mirroring technique is applied to such a audio signal processing system, it has not been possible to achieve a sufficient performance that can meet the need.
Furthermore, in a case where the audio signal processing system is used in an application, such as a public address system, vocal guidance system or intercommunication system, where there is not so great a need to continue outputting audio signals with no break, it is desirable to not waste audio signal transmitting bands (transmission channels) because the output audio signals may be interrupted for a certain time.